Within the field of memories, there is continuing interest in finding ways to increase the storage density and speed of memories. As the personal use of small devices gain popularity, the memory of these equipments has to be modified to match the function and design of these small devices. Particularly, as more and more data needs to be stored in the memory, the memory needs to have the capacity and speed to handle such demand.
The discovery of new phenomena of magnetoresistive (MR) and giantmagnetoresistive (GMR) effect provided a significant advancement in the field of memory technology. This phenomena demonstrated that resistance of multilayer thin film comprised of ferromagnetic layers sandwiching a conducting layer can change significantly depending on the direction of an external magnetic field.
GMR is observed in magnetic metallic layered structures in which it is possible to orient the magnetic moments of the ferromagnetic layers relative to one another. One such type magnetic metallic layered structure consists of a stack of four magnetic thin films: a free magnetic layer, a nonmagnetic conducting layer, a magnetic pinned layer and an exchange layer. Magnetic orientation of the pinned layer is fixed and held in place by the exchange layer. By applying an external magnetic field, the magnetic orientation of the free layer may be changed with respect to the magnetic orientation of the pinned layer. The change in the magnetic orientation generates a significant change in the resistance of the metallic layered structures. The resistance of the structure determines the logical value to be stored therein. that are based on GMR technology, use it to control a sensor that responds to very small rotations of magnetic orientation of the GMR free layer due to magnetization on the disk. However, the present use of this technology in disk drives require the disk to rotate and head to position on the track to be read, which requires more than 10 ms. The disk drive therefore is not utilizing the full potential of fast response time of the GMR which could translate into small access time. The access time using GMR in existing technology generally spans between 3ns–5 ns.
There is a clear need in the industry to develop fast memories which can be used in disk drives as well as small equipments.